Hot melt desiccant matrixes are complex mixtures of water absorbent material and inert organic binder, and they are extensively used in manufacturing of insulating glass units for windows and doors. Insulating glass (IG) units typically consist of two opposing panes of glass that are separated by a spacer along their edges. The panes of glass and the spacer sandwiched in-between are typically held in place by a sealant. In this application, desiccant matrix is deposited in and adhered to the spacer channel facing the interior of the IG unit. It plays the important function of removing moisture and any volatile organic compounds (VOC) that are sealed in the air space of the IG unit during manufacturing, and of absorbing infiltrated water vapor during use. Without desiccant, moisture and VOC will accumulate and eventually condense on the inner surfaces of the glass, causing formation of unsightly fog. The hot melt desiccant matrixes are particularly useful in conjunction with U-channel spacers, the formation and application of which are disclosed in prior art patents EP 475213 and U.S. Pat. No. 5,177,916. The entire patent disclosures of EP 475213 and U.S. Pat. No. 5,177,916 are herein incorporated by reference.
Various hot melt desiccant matrix formulations have been described in prior art patent literature. Meyer et al, for example, disclosed in U.S. Pat. Nos. 5,510,416 and 5,509,984 a hot melt desiccant matrix composition based on a film former consisting of a tackified polyisobutylene/amorphous poly-α-olefin (APAO) blend and an inorganic absorbent. The composition is claimed to function well in desiccating the air space of IG units.
Spinks, in U.S. Pat. No. 6,112,477, disclosed a hot melt desiccant matrix composition having a resin component and an absorbent material; the said resin component was selected from the group consisting of a linear ethylene/alpha-olefin interpolymer, a block copolymer, liquid polybutene or mixtures thereof in combination with APAO or linear ethylene/alpha olefin interpolymer. Optional polyisobutylene or butyl rubber could also be added to the above basic polymer composition.
Chu, in U.S. Pat. Nos. 6,180,708 B1 and 6,777,481 B2, also disclosed a similar resin/desiccant composite composition wherein the resin component contained a wax. The wax was said to be crucial for high absorbent loading.
While some of the existing formulations have significant commercial use, they all suffer from different flaws or shortcomings. The most noticeable is the lack of cold resistance. These compositions tend to become brittle at low temperatures and consequently lose adhesion to the spacer material. The loss of adhesion can cause the desiccant matrix to dislodge and fall off the spacer channel, thereby resulting in costly product liability claims from the end user. The polyisobutylene-based compositions of '416, '984 and '477 patents also have desiccant loading limitations due to the high viscosity of the organic binder system. Because the absorbent is the only active component in the matrix, it is highly desirable to maximize its content. Unfortunately, when the loading level of absorbent reaches about 45% by weight, the viscosity of the matrix usually shows an abrupt increase and the material can become non-pumpable with existing conventional means. This problem is especially prominent in polyisobutylene-based formulations. A need, therefore, exists for a novel hot melt desiccant composition that can overcome the above-mentioned shortcomings and restraints of the prior art compositions.